This invention relates to a method for measuring carboxylate anion present in used automotive and heavy duty engine coolants where it functions as a corrosion inhibitor and to a test kit for carrying out the method.
Automotive engine cooling systems contain a variety of metals and metal alloys such as copper, solder, brass, steel, cast iron, aluminum and magnesium. The vulnerability of such metals to corrosive attack is high due to the presence of corrosive liquids and various ions as well as the high temperatures, pressures and flow rates characteristic of engine cooling systems. The presence of corrosion products within a cooling system can also interfere with heat transfer from the engine combustion chambers which may subsequently cause engine overheating and engine component failure.
Corrosion inhibitors are commonly added to engine coolants, e.g., silicates are added to provide aluminum protection, nitrites are added for cast iron protection and azoles may be added for copper and brass corrosion protection and to assist in the protection of iron and steel. All corrosion inhibitors employed in automotive antifreeze/coolant formulations are gradually depleted by use. The life expectancy of most coolants is about one to three years due to the progressive depletion of the corrosion inhibitor component(s). Carboxylic acids in the form of their salts have been incorporated into engine coolants to provide a greater degree of corrosion protection than other known types of corrosion inhibitors. Carboxylates are superior due to their slower depletion rates compared with other corrosion inhibitors. The life expectancy of carboxylate-containing coolants are typically five years or more.
For proper coolant maintenance, the engine operator should routinely monitor coolant levels to determine that the coolant is providing suitable boil and freeze point protection. To maintain adequate levels of corrosion inhibitor, it is also essential that the engine operator continually monitor corrosion inhibitor levels and replenish the same as the circumstances require. Replacement of the entire coolant may be required when severe deterioration or contamination occurs.
Quick test methods are available for determining corrosion inhibitor contents, e.g., nitrite content, molybdate content, etc., of used engine coolant which involve immersing a test strip in the coolant which produces a color change that can be related to the corrosion inhibitor level. A low reading for the corrosion inhibitor indicates that corrective action should be taken to restore protection, e.g., the use of supplemental coolant additives or extenders to restore specific corrosion inhibitor levels for sufficient protection. Test methods are also available to determine that corrosion inhibitor levels do not become too high when supplemental coolant additives are used to restore corrosion inhibitor levels.
In use, carboxylate corrosion inhibitors deplete at a slower rate than other known inhibitors but, over time, may become contaminated by dilution with other manufactured engine coolants or water following coolant top-off. In order for the carboxylate corrosion inhibitors to provide adequate corrosion protection, their levels in used automotive and heavy duty engine coolants must be periodically determined.
Carboxylate anion present in used engine coolant can be analyzed by a well-equipped laboratory employing chromatographic techniques. However, these procedures are expensive and time consuming. Accordingly, there exists a need for an inexpensive, expeditious and reliable method for determining carboxylate anion levels present in used automotive and heavy duty engine coolants which lends itself to being carried out in the field with a minimum of technical expertise.